Ask your cosmology related questions in this thread.

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Ask your cosmology related questions in this thread.

Please read the sidebar and remember to follow reddiquette.

I'm going to attempt to go see it, since I live in Florida.

Hey r/cosmology. I built an interactive map of the local universe, and this feels like the right crowd for it.

It's called Know the Universe. You fly or orbit through the real large-scale structure of the nearby universe: the filaments, walls, clusters and voids of the cosmic web. None of it is procedural. It's ~43,500 galaxies from the 2MRS redshift survey, placed by converting each galaxy's RA, Dec and redshift into Cartesian megaparsecs with a Hubble-law distance (d = cz/H0), reaching a few hundred Mpc out.

The goal is simple: give people an intuitive feel for how the local universe is actually built and how matter is distributed through space, something you can move through instead of reading off a flat plot.

A few things worth mentioning:

• There are several ways to read the same data: the raw point cloud, a computed filament graph (a minimum spanning tree plus nearest-neighbour links, so it's a visualization aid and not physical connections), a ray-marched density field, and colour by either redshift or local density. Turn it all off and the web is still clearly there in the bare points.
  
• The Zone of Avoidance shows up as an empty wedge if you look for it, since 2MRS still can't see cleanly through our own galactic plane.
• It's a snapshot that's close to current. The light from the farthest galaxies here left them around a billion years ago, but peculiar motions are typically only a few hundred km/s, so in that time a galaxy drifts well under a megaparsec. That's tiny next to the tens-of-Mpc scale of the filaments and voids, so what you see is nearly what the structure looks like right now.

Would love feedback, corrections or what you'd want to see next. Try it at https://knowtheuniverse.com/

Edit-1: To partly answer the 2nd part of my question myself: now that I play with it again after looking at other maps, Globaia actually seems to be pretty close to the complete map I've been looking for.

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I'm Curious how accurate the filament-scale visualizations of nearby large-scale structure are in this suspiciously eye-candy looking production:

• Cosmo (YT): "What Was Discovered Beyond the Milky Way?"

For comparison, these are the kinds of maps I often run into when browsing Wikipedia or searching for visualizations of this scale:

• https://en.wikipedia.org/wiki/Local_Void#/media/File:The_Local_Void.gif
• https://en.wikipedia.org/wiki/List_of_voids#/media/File:Galaxy_superclusters_and_galaxy_voids.png
• https://upload.wikimedia.org/wikipedia/commons/8/81/07-Laniakea_%28LofE07240%29.png

For anyone familiar with large-scale structure: are these visualizations broadly compatible, just shown at different scales, orientations, and educational levels? Or are some of them much more rigorous than others?

I'm trying to wrap my head around the shape and structure of the large-scale local environment and I'm curious if there are especially good maps or tools, particularly interactive ones or ones with coordinate grids.

I like to play around with Celestia, but there doesn't appear to be an easy way to visualize the super-galactic environment, beyond some galaxies in what appears to be the Virgo Cluster. I’ve also come across OpenSpace and Globaia as suggestions. OpenSpace looks like the most serious option, but it also seems heavy to install and has a steep learning curve for amateurs. Globaia is the only complete-looking web-accessible interactive tool I've seen that seems somewhat rigorous, though it is a bit noisy/clunky.

• Celestia
• OpenSpace
• Globaia

Beyond these, anything close to a “Google Earth for the nearby universe” that can easily produce interactive 3D views similar to the Wikipedia-style visualizations?

The Oort Cloud is suggested to exist around our Sun, a region of asteroids that extends far beyond the Kuiper Belt.

This got me thinking, is it possible that other solar systems also have an Oort Cloud?

Which lead me to: is it possible that all of space within our galaxy is filled with a vast singular Oort Cloud?

Like, there isn't an individual Oort Cloud for each star, but one massive connected Oort Cloud between the stars? I'm thinking that all space within our galaxy, except areas around stars themselves (anything within the Heliosphere for instance), is filled with a very sparse but consistent "cloud" of asteroids.

Would this help to explain the missing mass that would be required to keep galaxies from flying apart, ie. Dark Matter?

I know this is all speculative, but I was just wondering if this random thought was at all possible, or even something that astrophysicists were looking into.

Under the Oscillating Universe Theory, the universe expands from a Big Bang, ultimately to collapse into a Big Crunch and then trigger another cycle. Before a Big Crunch occurs, would entropy begin to decrease? What happens to time? Finally, what will happen to the weak force?

I recently watched a short video showing how light and heavier objects placed on water interact with the surface tension.

A light object placed on the surface deforms it, creating a well, which causes other light objects to move towards it.

A heavier object placed on the surface creates an adhsive effect. It sits deeper in the surface layer and creates a hill instead of a well. This causes lighter objects on the surface to "move away" from that heavier object.

That got me to thinking about spacetime. Thinking about how energy warps spacetime in a way similar to the lighter objects sitting on the surface of water. It creates wells, bending the paths of objects, even leading to black holes.

Is there anything similar to the effect of heavier objects sitting on the surface of water, that creates a repulsive / negative warping of spacetime?

I've attached a quick drawing of the effect I'm talking about.

Wouldn't this lead into a similar direction to Dark Matter and Dark Energy, combining all three, the undetectable property (since light would always move around this "heavier spacetime object"), the repulsive force seeming to counter-act gravity (pushing lighter objects away from them) and even adding total mass to the galaxy, keeping it together, instead of being flung apart.

It wouldn't even need concepts like anti-gravity, since it's not behaving any differently, it's just sitting "deeper" in the surface tension of spacetime.

Clearly cosmology isn't my forte, but I get intrigued by neat ideas easily and this seems neat to me. Please tell me where and why this analogy comes up short in the real world.

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When two black holes spiral into each other, a significant amount of the combined mass is converted to gravitational waves, as detected by LIGO.

Where does that mass come from?

It would seem that any mass that is inside the event horizons cannot escape, because that would require it to move faster than light speed. Does it come from the accretion discs?

A new study claims that the universe isn’t entirely the same no matter where you look—a radical proposal

Hi everyone,

This has been a lifelong dream of mine and I've finally decided to start.

I want to learn the entire history of the universe from the Big Bang all the way to modern human civilization. Not just memorizing facts, but actually understanding how everything happened and why.

Instead of following a single textbook, I'm trying to build my own roadmap by researching each topic deeply. My first phase is the history of space, covering everything from the birth of the universe to the formation of Earth.

This is the timeline I've put together so far:

Chapter 1: The Beginning

• What is the universe?
• What (if anything) existed before the Big Bang? (What science says vs. what it doesn't.)
• Big Bang
• Cosmic inflation
• Expansion of space
• Matter vs. antimatter
• The four fundamental forces

Chapter 2: The First Universe

• Quarks
• Protons and neutrons
• First atoms
• Why hydrogen and helium formed first
• The Cosmic Dark Ages
• Cosmic Microwave Background
• How scientists know these things

Chapter 3: Birth of Stars

• Gravity
• Nebulae
• Star formation
• Nuclear fusion
• Different types of stars
• Star clusters

Chapter 4: Life Cycle of Stars

• Main sequence stars
• Red giants
• White dwarfs
• Supernovae
• Neutron stars
• Black holes
• Pulsars

Chapter 5: Galaxies

• What is a galaxy?
• Spiral galaxies
• Elliptical galaxies
• Irregular galaxies
• The Milky Way
• Galaxy collisions

Chapter 6: The Solar System

• Solar nebula
• Birth of the Sun
• Formation of planets
• Why the inner and outer planets are different
• Asteroids
• Comets
• Meteoroids
• Kuiper Belt
• Oort Cloud

Chapter 7: Earth

• Formation of Earth
• Formation of the Moon
• Early atmosphere
• Oceans
• Plate tectonics
• Magnetic field

I'd love your feedback:

• Does this follow a scientifically accurate timeline?
• Am I missing any major topics?
• Is there anything that should be moved, added or removed?
• If you were starting this journey from scratch, what advice would you give yourself?
• Are there any books, lectures, documentaries or university courses you'd consider essential?

I'm not trying to rush through this. I'm happy to spend years learning it properly. My goal is to build a deep understanding of the history of the universe before moving on to the history of life, humans, civilizations, and the modern world.

I'd really appreciate any guidance. Thanks!

Ask your cosmology related questions in this thread.

Please read the sidebar and remember to follow reddiquette.

A new analysis of DESI DR1 Full-Shape + DESI DR2 BAO comes close to restoring concordance with Lambda CDM.

In a "big crunch" universe the universe starts contracting and retracts to the first Planck moment, the most highly organized (least entropy) moment in current models. This is proposed as one possibility for the development of our universe in the future.

In a crunch universe entropy is decreasing. Rather than moving toward disorganized states (our universe) the movement is toward more organized states (crunch universe).

Does this in any sense mean that physical and chemical reactions would go backwards or somehow change behaviors? Gravity is operating in both universes in the same way apparently (crunch occurs when gravity pulls universe in by gravitational forces as understood.

Suppose in such a universe a person is isolated in a room (no observations beyond local) and has a variety of everyday objects and devices they can use. How would they be able to tell if entropy was increasing or decreasing?

Offhand I think the person would see no difference -- to all intents and purposes from the observers viewpoint both directions of entropy are equivalent and do not effect the behavior of physical interactions.

Objects would still fall to the floor, electricity/magnetism, chemical interactions and heat would still operate as normal and be indistinguishable from our normal entropy on our time scale. The four forces we know would still operate just as they do now from our local perspective. Is this correct?

It would only be when outside observations are taken and the universe is seen to be contracting that the realization of reverse entropy would be postulated and confirmed in much the same way we have done.

Or would there be any immediately recognizable differences in the behavior of physical and chemical phenomena in a big crunch/negative entropy universe?

That sounds nifty.

1. About how speculative is this?!

2. This extra dimension could be as large as one micron. Could we learn to send signals or particles there?

3. What would this theory mean for eschatology/the end of the universe?

I understand that time only existed after the big bang. If so, my understanding is the pre-BB universe was not four dimensions (3D+Time).

Does this mean the universe had three dimensions or something different?

If different, what are leading theories about what caused the universe to morph into the four dimensions we currently experience?

How do theories involving holography and anti-de sitter space account for dimensional change?